No idea, but the machining of those recesses, if you can call it machining, seems pretty crude and uneven compared to the rest of the frame. The one on the left side almost looks like something wedge shaped is protruding from it. But it could be the lighting. The top lever appears it may operate in similar fashion to the earlier pivot-lever Syracuse Lefevers.
It would be interesting to see a photo of the breech end of the barrels and the extractor to see what may mate up with that portion of the standing breech.
